Modern advanced machines such as semiconductor manufacturing machines are becoming more reliant on a multi-stage system in which an X-Y stage is allowed to move in both an X-direction and a Y-direction in a horizontal plane also has aboard a Z stage that can go up and down in a Z-direction perpendicular to the horizontal plane. Correspondingly, the Z stages of the sort recited just above are seeing growing demands for high precision travel, with even made slim or compact in construction and tough in stiffness. Besides being used for a work table of a machine tool to make vertical position-control of any workpiece carried on the work table, the Z stage unit like this one stated earlier is now built in a diverse machines including semiconductor manufacturing machines, assembly machines, inspection instruments, conveyor systems, and so on. The Z stages are now finding increased applications as the technology advances. Moreover, the Z stages are used in a way mounted on the X-Y stage systems to provide three-dimensional position-control stage systems.
A prior vertical position-control like the Z stage stated earlier is disclosed in, for example, Japanese Patent Laid-Open No. 48064/1999 in which a slantwise platform is mounted on top of the horizontal table and there are provided a linear motion guide unit having a first guide rail to move the horizontal table relatively to a machine base and another linear motion guide unit having a second guide rail lying on a inclined surface of the slantwise platform to get the Z stage to go up and down as the horizontal table moves.
The prior vertical position control as recited above, however, needs many parts or components, plenty of time to assemble every part into a stage unit, and also not only increases in stage dimensions but is not quite good enough to comply with the demand for highly precise position-control in years.
Another prior art of the vertical position-controls is disclosed in, for example Japanese Utility Model laid-Open No. 53042/1994, in which a ball screw- and lead nut arrangement is employed to get a table system going up and down. The system table can move in a vertical direction with the help of a slantwise surface. The table system is composed of a machine base, a first table mounted on top of the machine base for movement in a horizontal plane and made inclined on a top face thereof, a motor to drive the first table, a second table installed for movement along the inclined face of the first table, another motor to force the second table, a lead nut mating with a first ball screw, the lead nut being secured to a bottom of the first table having the inclined surface on the top thereof, and a second ball screw mounted on the inclined surface to move up and down the second table.
With the prior table system constructed as recited earlier, the lead screws are provided for tables, one to each table, to get the tables moving back and forth with carrying the loads thereon. This prior art, because of needing two driving mechanisms to be built therein, results in increasing overall height of the table system. Moreover, it would be tough to ensure the lead screws enough in stiffness to carry whole load with making certain of steady position-control and travel of the tables. This means that the prior table system as recited above would be unsuited for the worktable in the machine tools, which need precise position-control in machining operations. Thus, such table systems, although less in number of parts or components and ready for carrying some relatively lightweight instruments, could not be expected to make certain of precise position-control when carrying any heavy instruments because the lead screws are exposed to directly stand up to the heavy load, and therefore would be limited in their use.
Disclosure of U.S. Pat. No. 5,427,349 teaches an adjustable base assembly in which an upper wedge plate assembly is raised or lowered with using a vertical adjustment screw including left and right threaded portions, like a turnbuckle. With the prior base assembly recited above, a pair of wedge blocks is flanked by the upper and lower wedge plates, with their upper wedge faces coming into sliding engagement with the downwardly converging faces of the upper wedge plate while their lower wedge faces coming into sliding engagement with the upwardly converging faces of the lower wedge plate. Turning the screw moves the wedge blocks towards or away from each other to raise or lower the upper wedge plate relative to the lower wedge plate.
The base assembly so constructed as to rely on surface-to-surface sliding engagement stated earlier is not ready for demands on highly precise position-control and also fails to manage delicate operations.
A double linear guide system is known as disclosed in, for example Japanese Utility Model Registration No. 2505894, in which the guide rail is provided with four raceway grooves extending lengthwise in parallel with one another. With the double linear guide system cited above, first and second sliders fit over the guide rail, which has on widthwise opposing sides thereof four raceway grooves extending lengthwise in parallel with one another. The double linear guide system can not find its way in the vertical position-control because the sliders are allowed to move only in parallel with one another. Other Z stage system is known, in which there is provided a slantwise base with V-shaped raceway grooves on sides thereof, which is pinched by a pair of track pieces to undergo prestress to be guided. However, the Z stage of the sort stated earlier, because of needing to prepare a pair of track pieces separately, is large in number of the required parts or components and correspondingly harder to assemble them, having to go through troublesome process of attempting to get alignment to make sure of precision on assembly.